CICIND REPORT Vol. 28, No. 1

135

Coal fired Castle Peak Power Station in Hong Kong modifies 250 m reinforced

concrete chimney with four steel flues

CLP Power, a subsidiary of China Light & Power, is the lead-

ing supplier of electricity in Hong Kong. CLP Power’s Castle

Peak Power Station (figure 1), one of the largest coal firing

power stations in the world, has four 677 MW units that were

commissioned between 1985 and 1989. Running at over 38%

efficiency at full load, the Castle Peak B units are a key gener-

ating asset for the Hong Kong economy.

To help improve air quality, it was decided in 2006 that all

four units of Castle Peak B Power Station should be equipped

with highly efficient wet limestone flue gas desulphurization

plants.

The four units of Castle Peak B use a common 250 m high

reinforced concrete chimney, which contains four corten steel

flues each with a diameter of 6.6 m. The steel flues were origi-

nally constructed without an internal lining. CLP Power recog-

nized however that following the FGD retrofit, the flue gas

temperature would drop well below its acid dewpoint, result-

ing in the need for a chimney flue lining system.

With the FGD working, the treated flue gas will be reheated by

Gas-to-Gas heaters to 80˚C. Graph 1 shows the determination

of the sulphuric acid dewpoint according to the Haase-

Borgmann formula. For a flue gas with 10 mg/Nm3 SO3 and 8

% water, the expected acid dewpoint will be 122˚C. The flue

gas temperature in the steel flues will therefore be 40˚C under

sulphuric acid dewpoint.

Graph 2 shows the relation between the temperature and the

concentration of condensed sulphuric acid.

Albert de Kreij

Albert de Kreij joined Hadek Pro-

tective Systems in 1989. He has

been closely involved in a number

of projects with the use of Boro-

silicate Glass Block Linings espe-

cially in wet stack operation con-

ditions.

Figure 1 : Castle Peak B Power Station

Graph 1: Determination of sulphuric acid dewpoint

according to Haase-Borgmann formula

Graph 2: Variation of condensed sulphuric

acid concentration with temperature

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CICIND REPORT Vol. 28, No. 1

With a flue gas temperature of 80˚C, the estimated concentra-

tion of sulphuric acid will be 63 %. The sulphuric acid concen-

tration will be highly corrosive. The flues must be lined to

resist the corrosive conditions.

Following an evaluation of different chimney flue lining tech-

nologies, CLP Power selected the Pennguard Block Lining

System, using 51 mm thick Pennguard Block 55 (Graph 3).

The Pennguard linings were installed in all four flues during

planned boiler outages, each about 70 days long, in 2008, 2009

and 2010.

CLP Power awarded the lining installation contract to Bal-

anced Engineering & Construction Pte Ltd (BEC) from Singa-

pore. To ensure a safe, timely, high quality completion of the

works, BEC paid close attention to several key aspects.

1. Access and weather protection

A strong platform, with a full floor and a fast, separate hoist

for materials supply was built, to ensure optimum access to all

steel surfaces, as well as an uninterrupted supply of Pennguard

materials to the installation crews (figure 2). The top of the

chimney was sealed off with a temporary roof (figure 3).

2. Surface preparation

Gritblasting up to 250 m high was made possible by a single

336 m3/hour compressor (figure 4) placed on ground level,

with 3 blast pots placed on the support floors within the chim-

ney windshield.

Graph 3: Schematic cross section of the

Pennguard lined steel flues

Figure 2: Work platform, separate hoist

for lining materials

Figure 3: Temporary roof

Figure 3: 336 m3/hour compressor

3. Condition of steel plate and welds

Pennguard linings offer a great advantage for lining used steel

flues that were not originally fabricated as “fit-for-

lining” (figure 4) : small imperfections in welds, such as rip-

Figure 4: Protruding welds and slight roughness in used

steel flues are acceptable for the

Pennguard Block Lining System

CICIND REPORT Vol. 28, No. 1

137

ples, protrusions and pinholes can be left uncorrected and even

slight pitting in the steel plate is not a problem.

4. Short time available for

lining installation

The Pennguard lining installation work was performed by two

teams, each with 8 trained brick layers, working in two shifts

per 24 hours (figure 5). The typical productivity per day was

250 m2.

5. Quality Assurance during

lining installation

All works were supervised by Hadek QA Inspectors (figure 6).

One QA Inspector attended during surface preparation. During

installation of the Pennguard lining, one Inspector was present

during the day shift and a second Inspector worked during the

night shift. As on most Pennguard lining projects, Hadek per-

formed intensive, systematic QA Supervision, allowing any

defects to be identified and corrected immediately.

Cold spots: a fundamental problem for steel chimneys and

chimney flues that is eliminated by the use of Pennguard

linings

For structural stability as well as for construction purposes,

every steel chimney / steel chimney flue has stiffeners on its

outside. In these areas, the steel is much thicker than the stan-

dard plate thickness and it is often difficult to apply an effec-

tive thermal insulation.

These stiffeners generate “cold spots” on the inside of the

chimney flue, where excessive condensate formation can take

place especially during start-ups and low load operation (graph

4).

Figure 5: Pennguard lining installation

Figure 6: All works were supervised by

Hadek QA Inspectors

Graph 4: Situation prior to Pennguard lining installation

and removal of external insulation

Graph 5: Situation following Pennguard installation

and removal of external insulation

The use of thermally insulating Pennguard linings on the inside

of steel flues eliminates this problem. The Pennguard lining

system will provide effective thermal insulation in all areas of

the flue, even where the outside flue surface is covered with

external stiffeners (graph 5).

Summary and Conclusion

Operating conditions are corrosive regardless of reheat;

Pennguard linings successfully installed in 70 day

outages;

Lining system tolerance of steel plate and weld imper-

fections prevented time consuming repair works.